Set top terminal devices commonly in use in existing cable television systems have a number of limitations. First, the devices are limited to processing of analog television signals. Also, cable television terminal devices are generally "dumb" devices having a limited set of functionalities constrained by the hard wired programming of the internal microprocessor controlled device. Essentially all cable television terminal devices respond to a selection input from the subscriber, tune to a selected channel available on the cable television network, decode the video program material if scrambled, and provide output signals compatible with a standard television receiver.
Enhanced cable television terminals provide some additional features, such as graphics overlay capability and two way communication of control signalling to and from headend terminal devices. Although such improved terminals facilitate some enhanced services, such as home shopping and purchasing, the performance of these cable television set-top terminals is still limited to analog decoding. Also the range of services is still limited by the hard wired capabilities of the microprocessor within the set-top terminal devices.
Proposals have been made to download computer executable code over cable television networks. In particular, U.S. Pat. Nos. 5,051,822 and 5,181,107 both to Rhoades disclose a terminal device connectable to a cable television network and a telephone line. A subscriber requests a video game or other software stored in a remotely located software storage center by operating the terminal to establish a bi-directional telephone link with the remote storage center. The center transmits the encoded software program together with the terminal identification code as a digital bit stream over a television broadcast channel. The terminal requesting the software monitors all digital bit streams on the broadcast channel but receives only the software program addressed to it, i.e. only after identification code validation occurs. Once reception of all the software data is complete, the terminal acknowledges receipt to the remote storage center and drops the telephone line. The encoded software program is decoded, and the terminal provides a display informing the subscriber that the game or other program is ready for use. The terminal also offers the subscriber the means to interact with the software, e.g. play the game, using contemporary gaming control or input devices. While the Rhoades terminal structure does provide enhanced capabilities, such as video games and home shopping, the display functionality controlled by the downloaded software is limited to computer displays generated in response to the software, there is no direct interaction of the received software with any video program carried on the cable network. The downloaded software does not control further interactions with the storage center. Also, the video transmissions on the cable system are analog, and a separate telephone connection is required for selection inputs to the central storage facility. Furthermore, the terminal device apparently can receive software from the storage center of only one service provider.
Some prior art systems do permit downloading into the cable television decoder itself, however, at least initially, this downloading of information into the decoder was limited to information controlling the decoding of the television program signals, e.g. a key word used in a descrambling algorithm. Dufresne et al., in U.S. Pat. No. 4,623,920 teach a specific scheme for addressing data transmissions over a cable television network to groups of terminals or to individual terminals. The addressed data sent from the head end can include an option table of signals for controlling descrambling of available television programs, data to enable operation of a cable TV converter, or software for operating a peripheral microcomputer separate from the cable television terminal device. The Dufresne et al. terminal is limited to reception of data from only one service provider, i.e. the provider operating the cable TV network. Also, the services provided through the terminal are limited in that the downloaded data apparently does not alter or control the terminal functionality for further interactions with the provider through the network.
Another example of a software downloading system is disclosed in U.S. Pat. No. 5,440,632 to Bacon et al. In this system, the headend of an analog cable television system downloads an `operating system` to each set-top terminal device. Again, the one service provider operating the headend supplies all downloaded code.
Recently, several different wideband digital distribution networks have been proposed for offering subscribers an array of video services, such as Video On Demand. The following U.S. Patents disclose representative examples of such digital video distributions networks: U.S. Pat. No. 5,253,275 to Yurt et al., U.S. Pat. No. 5,132,992 to Yurt et al., U.S. Pat. No. 5,133,079 to Ballantyne et al., U.S. Pat. No. 5,130,792 to Tindell et al., U.S. Pat. No. 5,057,932 to Lang, U.S. Pat. No. 4,963,995 to Lang, U.S. Pat. No. 4,949,187 to Cohen, U.S. Pat. No. 5,027,400 to Baji et al., and U.S. Pat. No. 4,506,387 to Walter. The terminal devices in these digital networks are still limited functionality devices. In these networks, the digital terminal devices still only receive selection inputs, transmit selection signals upstream to the source of the video materials, receive downstream video transmissions, decompress the digitized video materials and convert to analog form, and provide appropriate signals to a television receiver. One example of such a digital video distribution network and the terminal device for such a network, disclosed in Litteral et al. U.S. Pat. No. 5,247,347, will be described in more detail below.
U.S. Pat. No. 5,247,347 to Litteral et al. discloses an enhanced public switched telephone network which also provides a video on demand service to subscribers over the public switched telephone network. A menu of video programming information is displayed at the subscriber's premises by a set-top terminal and a TV set. The subscriber may transmit ordering information via the public switched telephone network to the independent video information providers. Video programming may be accessed and transmitted to the subscriber directly from a video information provider (VIP) or through a video buffer located at a central office (CO) serving the subscriber.
Connectivity between the central office and the subscriber for transmission of video data is provided by an asymmetrical digital subscriber line (ADSL) system. ADSL interface units at the central office multiplex digital video information with voice information to be transmitted to the subscriber and support two-way transmission between the subscriber's line and the X.25 packet data network of one or more control channels. A complimentary ADSL interface unit at the subscriber's premises separates downstream video control signals and voice telephone signals from the line and multiplexes upstream control signals and voice telephone signals onto the line. The ADSL interface on the subscriber premises supplies the broadband digital data stream recovered from the transmission over the subscriber loop to a decoder unit in the set-top terminal. The decoder unit decompresses the audio and video data, and converts the digital audio and video to corresponding analog signals. The decoder can supply baseband analog audio and video signals to a television receiver, or these analog signals can be modulated to a standard television channel frequency for use by the television receiver.
The above detailed discussion of the Litteral et al. system shows that prior art digital distribution networks offer enhanced video services, but the terminal device functionality is still limited to program selection, decoding and display.
A number of suggestions have been made in the press regarding arrays of different services which will become available through broadband digital networks now popularly referred to as the "Information Super Highway". If a different VIP were to offer a different service, the VIP can limit the service to an interactivity with the subscriber essentially corresponding to the functionality available in the terminal device. This approach, however, limits the functional capabilities the new VIP may choose for the different service. Alternatively, the subscriber must buy another terminal device programmed or wired to function in accord with the VIP's new service. This second approach, however, forces the subscriber to purchase and connect up a different terminal device for each different service subscribed to.
From the above discussion it becomes clear that a need exists in the art for set-top terminal devices which process compressed, broadband digital audio/video information and are readily adaptable to perform a variety of related functionalities, as needed to facilitate a range of audio/video and interactive services offered by a large number of information providers.
In commonly assigned application Ser. No. 08/250,791 (and corresponding published PCT application WO/95/33338), it was suggested that software could be downloaded into the digital set-top terminal through a point-to-point connection through a digital broadband network, e.g. similar to that of Litteral et al. As disclosed therein, the software included at least customized applications programs for controlling terminal operation in a manner specified by any one of several information providers. It was also suggested that at least one party would operate a server to download operations system upgrades through a point-to-point connection.
The use of a full broadband channel dedicated to one subscriber for an entire interactive session, as in systems such as that disclosed in the application Ser. No. 08/250,791 (and WO/95/33338), places a heavy burden on network resources. Building a large capacity network to carry a large number of such individual sessions is prohibitively expensive. The alternative, providing a limited number of point-to-point links limits the number of subscribers who can access interactive services at any one time, making the interactive services commercially unattractive to the information providers. The need for level 1 and level 2 gateways further increases the cost and complexity of developing and deploying video dial tone networks having such point-to-point connectivity.
Also, some digital networks under development will have broadcast channels, but at least initially, will not offer point-to-point connections. The disclosure in the application Ser. No. 08/250,791 did not address problems of downloading software to terminals through digital broadcast networks.
In commonly assigned application Ser. No. 08/380,755, it was suggested that software, specifically software related to channel mapping functionalities and navigation through broadcast services, could be downloaded into the digital set-top terminal through a data carousel type cyclical broadcast. Such downloaded software consisted of one or more applications intended for wide general availability. The digital type set-top devices receiving such software were intended as open interface devices to which any provider offering such a download service could download the relevant data and executable code. The downloaded applications, however, provided relatively little interactivity.
Still frame services have been proposed for analog cable television systems to provide a limited capacity interactive service through a single broadcast channel of the CATV network. Some of the prior proposals for such services have utilized digital still frame encoding. However, the digital still frame technology was not compatible with the devices for receiving other signals on the CATV network, i.e. standard analog broadcast television signals. Consequently, a subscriber had to have a digital receiver for decoding the still frame signals separate and in addition to any cable decoder equipment needed to receive the analog channels. These terminals have not been adapted for use in all-digital broadband networks or to provide any associated digital video services. Also, such technologies intended for CATV networks are not readily adaptable to open architecture systems, such as the video dial tone networks disclosed in the above cited applications, for providing information services from multiple providers who operate independently of the network service provider.
Also, the various earlier proposals for software downloading have not adequately addressed issues relating to the interface between the resident software and the downloaded software. In an open video environment, such as a video dial tone network, where several providers offer a variety of software downloads through the network, the network operator must maintain the integrity of the network. In this regard, it is difficult for the network operator to police the downloaded software to insure compatibility with the network functionality. For example, if the downloaded software communicates with control elements of the network, the network operator must insure that the communications conform to accepted network protocol standards and relate only to accepted network operations, for example to avoid engaging a network node in an endless processing loop.
A need therefore still exists to adapt the digital video terminal devices and associated networks to provide interactive services in some manner which utilizes an acceptably low amount of bandwidth and still provides the user with the desirable highly programmable and dynamic interactivity. Also, a need exists for an interface between resident software and downloaded software that protects the network elements and maximizes network integrity.